Most conventional aerosol nozzle systems used for delivering and dispensing application media, such as insecticides, fertilizers and other chemical sprays, generate spray mists of liquid media droplets having sizes in the order of 100 to 500 microns, the sizes being measured across the diameters of the droplets. These conventional systems have dispensed application media in a variety of different ways, from localized misting systems in which the application media is dispensed as a mist directly into the ambient air to fall by gravity on a selected target area, to airstream transport systems where the mist is injected into an airstream, and the airstream is used to transport the application media to a more remote target location.
There are a number of different ways that prior art airstream type systems have introduced liquid droplets into an airstream. In one airstream type of sprayer used commercially in agricultural applications, for example, a number of liquid dispensing nozzles, usually four or six nozzles, are placed in equally spaced locations about the internal diameter of a high velocity airstream nozzle and arranged to extend radially inwardly into the airstream nozzle for dispensing application media droplets into the central portion of the airstream.
In recent years, it has been realized that droplets in the 100 to 500 micron size range have a number of disadvantages. Among other disadvantages, droplets of this magnitude of size have considerable weight, and for this reason, such droplets tend to fall to the ground when it is attempted to propel the droplets in an airstream generated by conventional spray delivery systems. Consequently, it is difficult to deliver droplets of this size to locations that are removed from the spray nozzle by substantial distances. Moreover, it has been discovered that, for contact insecticides that kill insects upon impingement, droplets in the 100 to 500 micron range provide substantial overkill, and consequently, the use of droplets of this size results in an inefficient and wasteful use of the insecticide.
In order to partially alleviate the disadvantageous consequences that flow from the use of such large droplets, spray nozzles have been developed that produce droplets having a size in the order of 1 to 60 microns. Liquid droplets in this size range are generally referred to in the industry as ultra low volume (ULV) droplets. Studies have shown that ULV droplet sizes are optionally sized for killing many types of insects with direct impingement insecticides, and droplets of insecticides in this size range are more effective in killing insects with substantially smaller amounts of insecticide. Further, these smaller droplet sizes can be carried more easily over substantially longer distances in an airstream than can droplet sizes in the 100 to 500 micron size range. Additionally, the use of such smaller droplets permits the dispensing of the application media in concentrated, undiluted form. Among other advantages, the dispensing of such chemicals in concentrated form eliminates the need to carry the additional volume and weight of water or other mixing media on the vehicle transporting the aerosol system. It further eliminates the need to expend the considerable energy required for dispensing water over long distances. Unfortunately, most conventional liquid dispensing nozzles cannot produce liquid droplets in the ULV size range.
Among other methods of producing and dispensing the small liquid droplets of application media, one commercially available nozzle system for dispensing droplets in the 60 micron size range has been designed to discharge droplets of chemical insecticide from a liquid nozzle located in the center of a high velocity airstream at the outlet of an airstream nozzle, and to use the airstream to carry the droplets of insecticide over substantial areas of farm fields to kill insects that are harmful to crops. In this system, a spray of chemical is metered at low pressure into a spinning rotating sleeve which delivers a narrow spectrum of droplets into a turbulent airstream. The outside of the cylinder has a series of radially outwardly extending blades, the pitch of which blades control the speed of the cylinder rotation. The rotational speed of the cylinder, in turn, controls the droplet size of the droplet dispensed into an airstream. The airstream, which is created by a centrifugal fan, then carries the droplets to a distal location. These and other types of insecticide dispensing systems have achieved some measure of success. Nevertheless, the chemical spraying and dusting machines of the prior art have been unable to apply insecticides effectively in many situations. Indeed, many situations place mutually contradictory requirements upon the dispensing systems. For example, it is often necessary to spray insecticides from portable misters transported on the bed of a small, light truck, and to penetrate through thick foliage with the spray. The need to penetrate the foliage precipitates the need to dispense the insecticide in an airstream having substantial velocity and airflow, a need that is usually fulfilled by using larger, heaver blowers. However, at the same time, it is often necessary to transport the insecticide dispensing system economically in lightweight vehicles to locations that are inaccessible to larger vehicles, and the size, space and expense of larger blowers is often prohibitive. Also, it is often necessary to apply insecticide in locations that are some distance from roadways, or other areas that are inaccessible to the spraying and dusting machines, even when they are mounted on small, mobile, lightweight trucks.
Dispensing the insecticide in small droplets reduces the weight of the droplets and makes it easier to carry the droplets over long distances. However, the light weight of these small droplets makes the airstream transport of the droplets highly susceptible to interference by the wind, and it is difficult, sometimes impossible, during even light wind conditions, to accurately transport the small, optionally sized droplets of application media in an airstream created by conventional insecticide dispensing systems. Consequently, if the insecticide or other application media is to be accurately applied in less than perfect weather conditions, it is necessary to protect the chemical spray against wind interference. However, most prior art aerosol sprayers and dusters, which have not been able to adequately control and target the application of insecticides or other application media sprays over long distances under even ideal conditions, are virtually inoperable under any wind conditions.